1. Field of the Invention
The present invention relates generally to a keypad assembly used as a data input unit in various electronic devices, and in particular, to a keypad assembly for selectively operating in a mechanical metal dome mode or a capacitive touchpad mode while achieving a reduction in volume.
2. Description of the Related Art
Electronic devices, in particular, portable electronic devices include a keypad assembly having one or more keytops as a data input unit. A user conveniently inputs alphanumeric or symbol characters and selects a desired function using the keypad assembly.
Recently introduced electronic devices have a variety of functions and become smaller, lighter, and slimmer in order to meet a user's demand. Accordingly, the keypad assembly has also become smaller, lighter, and slimmer while performing an equal or better function. In particular, in a mobile terminal the improvement of the keypad assembly is necessary.
A structure for a mechanical metal dome mode as an operational mode of the keypad assembly is constructed as follows: one or more metal domes are attached at predetermined contact points on a Printed Circuit Board (PCB) or a Flexible Printed Circuit Board (FPCB), a silicon keypad rubber with a predetermined thickness, on which corresponding protrusions are formed, is stacked on the PCB or the FPCB, and a keypad sheet or keybuttons are attached on the silicon keypad rubber.
A structure for a capacitive touchpad mode as an other operational mode of the keypad assembly is constructed as follows: films having corresponding electrodes cross each other on a FPCB to form a coordinate system, and a dielectric layer is interposed between the films. Accordingly, when a user touches the keypad assembly using the structure, capacitance at the touched position is changed, such that corresponding data are input by detecting the capacitance change.
Recently, a new keypad assembly for allowing the selection of the mechanical metal dome mode or the touchpad mode is introduced. For example, it is configured by stacking the structure for the touchpad mode on the structure for the mechanical metal dome mode and one of two modes is selectively used according to a user's selection.
In the structure described above, the structure for the mechanical metal dome mode is stacked on a PCB, a capacitive touchpad is stacked on the structure for the mechanical metal dome mode, and a keypad is stacked on the touchpad. Accordingly, the whole thickness of the keypad assembly having the above structure is increased, and an air gap generated between the keypad and the touchpad significantly degrades touch sensitivity and causes the keypad assembly to malfunction.